Find the derivative $of$ each function:

$1f(x)=x^7$

$2f(x)=x^{18}$

$3f(x)=x^{\frac{-1}{2}}$

$4f(x)=\sqrt[2]{x}$

$5f(x)=\frac{1}{\sqrt[\phantom{2}]{x}}$

$6f(x)=\sqrt[4]{x^3}$